Oil Contact Angle Research Articles

A trash-to-treasure strategy to upcycle abandoned masks to ultraelastic fiber aerogel

Masks are indispensable in our daily life, but the accumulation of abandoned masks has been increasing in landfills and incineration, causing serious environmental concerns. Here, we propose a trash-to-treasure strategy to reuse the hard-to-degrade polypropylene (PP) fibers in abandoned masks and introduce polyvinyl alcohol (PVA) as a binder to fabricate ultralight and ultraelastic PP fiber aerogel through a facile freeze-drying process. The fiber aerogel exhibits a highly porous structure with PP fibers closely bonded by PVA. Thanks to the overlapping structure of the PP fibers and the bonding effect of PVA, the fiber aerogel shows ultraelastic properties and can undergo repeated compression without any fatigue. The results further indicate that the fiber aerogel represents selective wetting behavior to oil and water with water contact angle of ca. 130° and oil contact angle of 0°, respectively. Owing to the highly porous, ultraelastic, and special wetting behaviors, the fiber aerogel demonstrates diverse potential applications in oil/water separation, thermal insulation, and pressure sensing. Briefly, the fiber aerogels can absorb diverse kinds of oils and organic solvents with an optimal oil absorption capacity high up to 27.5 g/g. The fiber aerogel can also be used as a heat-insulating material to reduce heat loss. Further, after being modified by conductive filler, the fiber aerogel can monitor various human activities in real time, including walking, knee bending, sitting, and lying. This study not only provides a new way to alleviate the difficulties of recycling abandoned masks but also proposes a novel strategy to prepare value-added multifunctional fiber aerogels.

The optimized microbial-induced calcium carbonate precipitation process to fabricate underwater superoleophobic mesh for efficient oil-water separation

Microbial-induced calcium carbonate precipitation (MICP) is an environmentally-friendly and easy operation technique for separating oil-water mixtures. However, the effect of environmental factors on the wettability and oil-water separation performance of MICP remains unclear. In this study, three primary factors including mineralization solution (MS) concentration, bacterial suspension (BS) concentration, and temperature were carefully investigated. Under these varying conditions, stainless steel meshes (SSM) were chosen as the substrates for the growth of CaCO3 precipitations. Experimental results demonstrate a strong dependence of the morphology and wettability of CaCO3 precipitations on these factors. Higher MS concentration and temperature contribute to enhanced hydrophilicity of CaCO3 coatings due to the increased surface roughness. The water flux of MICP-coated SSMs decreases with the increase of BS concentration, MS concentration, and temperature. The MICP-coated SSM obtained with MS concentration of 0.15 M, BS concentration of 0.1 × 108 cells/mL, and mineralization reaction at 25 ℃ for 24 hours demonstrated the optimal comprehensive performance, exhibiting underwater superoleophobicity with an underwater oil contact angle (UWOCA) exceeding 151°, an ultra-high oil intrusion pressure (> 3.0 kPa), ultrahigh flux (28,644 L m−2 h−1), and a preferable oil rejection rate (> 99.9%). Additionally, the as-prepared mesh exhibited superior anti-oil-fouling property and reusability, while concurrently demonstrating excellent chemical and thermal stability. This work contributes to advancing our knowledge of the influence of various environmental factors on the wetting characteristics of MICP and provides a feasible solution for the highly efficient and low-cost preparation of oil-water separation membranes based on the MICP process.

Rational designed of PVDF membrane based on surface modification of εPL anchored by PC for crude oil emulsion separation

For high-viscosity wastewater containing crude oil, the membrane material is easily clogged with contaminations, resulting in decreased flux and potentially loss of separation ability. In this study, a superhydrophilic/underwater superoleophobic PVDF membrane (PVDF-PC-εPL) was designed by the self-polymerization of proanthocyanidins (PC) and the grafting reaction of ε-polylysine (εPL), which showed a rough micro-nano structure without adding the inorganic particles. The PVDF-PC-εPL membrane displayed outstanding self-cleaning ability for high-viscosity crude oil, and the separation efficiency of the crude oil-in-water emulsion could be greater than 99.4%. The underwater oil contact angle (UWOCA) of the PVDF-PC-εPL membrane was 165°, after the PVDF-PC-εPL membrane had been exposed to air or water for 6 weeks, or soaked in different pH or seawater for 24 h, the UWOCA remained above 154° and the water contact angle was always 0°. The modification method on the PVDF membrane proposed in this study offers a fresh perspective and choice for preparing the oil-water separation materials.

Effect of Surface Roughness of Pistia Leaves Inspired Surfaces on Oil Contact Angle and Coefficient of Friction under Lubricated Condition

Biomimetics field is getting more interest in engineering purposes. The plant surface roughness existing in nature such as in leaves can be mimicked into artificial technologies. Basically, the surface structures have micro and nano scales in nature and possess properties of interest. Pistia leaves for example have intrinsic of tribology application which have rarely explored. In this study, a preliminary work on 3 types of Pistia leaves inspired surface-based polymer have been conducted to look at effect of surface roughness towards contact angle (CA) measurements and coefficient of friction (COF) under lubricated condition. The surface characteristics were also examined using Variable Pressure Scanning Electron Microscope (VP-SEM). Two different oils namely palm oil and palm oil + TiO2 were tested on the Pistia leaves inspired surface to measure the CA and COF. It was found that both types of palm oils had distinct CA values and COF towards surface roughness of the Pistia inspired surfaces. A maximum difference of CA and COF were recorded in CA and COF values. The different nanocomposite of Pistia leaves inspired surface were found to affect for both parameters CA and COF under lubricated condition.

One-step candle soot-PDMS dip-coated superhydrophobic stainless steel mesh for oil-water separation

We presented a superhydrophobic stainless steel mesh (SSM) developed by facile one-step dip coating of candle soot (CS)-polydimethylsiloxane (PDMS) using chloroform as solvent for effective and durable oil-water separation. SSM dip coated with chloroform solution of 200 mg CS and 0.5 mL PDMS yielded water contact angle (WCA), oil contact angle (OCA) and sliding angle (SA) of 162 ± 2°, 0° and 4 ± 1°, respectively. In series of oil-water separation studies, superhydrophobic mesh revealed >98 % separation efficiency with high separation flux of 7810 L·m−2·h−1. The superhydrophobic mesh revealed excellent mechanical, chemical and thermal durability.

Nano-SiO2 based anti-corrosion superhydrophobic coating on Al alloy with mechanical stability, anti-pollution and self-cleaning properties

Improving the corrosion resistance of widely used Al alloys is important for expanding their industrial and marine applications. Structural fragility and preparation cost have always been key factors for restricting anticorrosive application of extensively-reported superhydrophobic surface. In order to try and fight that, combining with polyurethane (PU) adhesion agent, 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PFDTES) was encapsulated around nano-SiO2 ceramics for robust coating in place of conventional structure preparation strategy on Al alloy surface. Such low-cost one-step air-spraying SiO2@PFDTES@PU coating was prepared by 0.03 g nano-SiO2 ceramics addition, 100 μL PFDTES and 0.25 g PU with the highest water contact angle of 168.34° ± 2.72°, a rolling angle of 4.02° ± 2.08°, and a propylene glycol oil contact angle of 156.52° ± 3.35°. FE-SEM, laser confocal microscopy, EDS and XPS were used to investigate micro-nano morphology and chemical composition of the coating. Meanwhile, the electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements showed that as-prepared coating exhibited larger capacitive arc diameter, enhanced charge transfer resistance, larger |Z|0.01Hz value, positive shifting Ecorr and significantly reduced Icorr, thus demonstrating a significantly improved corrosion resistance. In addition, sandpaper friction experiment was used to evaluate the mechanical stability of the fabricated superhydrophobic coating. Ultimately, its resistance to solid/liquid contamination and self-cleaning ability were also systematically assessed. This work provides strong technical supports for industrial and marine applications for such low-cost, wear-resistant and anti-corrosion coating.

A novel and simple fabrication method for a biomimetic-inspired lath-structured ceramic microfiltration membrane for the treatment of oil-in-water emulsions

Ceramic membranes have been widely explored as competent alternatives to traditional polymeric membranes for treating oily wastewater. Despite the exceptionally high rejection rate (>90 %) of oil–water (O/W) emulsions, membrane fouling is an inevitable phenomenon that limits the separation efficiency of ceramic membranes. Biomimetic technology, known as the lotus effect, has attracted attention as a groundbreaking method for reducing membrane fouling. However, it is difficult to control the nanostructured surfaces of ceramics, while polymer fabrication is facile. In this study, we developed a novel and simple method to fabricate an α-alumina (Al2O3) microfiltration (MF) membrane with a Nepenthes pitcher plant-like microstructure. The surface roughness of the biomimetic membrane was 286 nm, which was approximately twice that of a normal ceramic membrane. Accordingly, the oil contact angle increased from 88.84 to 128.51°. The novel biomimetic membrane showed high efficiency with an emulsion permeability of 44.1 LMH/bar, a flux recovery of 90.91 %, and an oil rejection rate of 99 %.

Amino-functionalization of tungsten oxide nanoparticles for stable decoration in the active layer of alumina-supported inorganic-organic hybrid membrane with super-wettable and photocatalytic self-cleaning surfaces for crude oil-in-water emulsion separation

The ceramic membrane was hybridized with an amino-functionalized inorganic metal oxide and organic polymer to achieve the optimal oil and water surface wettability and photo-catalytic self-cleaning capability. The resulting membrane was used for the treatment of crude oil-contaminated wastewater under cross-flow filtration mode. The fundamental functional material, tungsten oxide nanoparticles (NH2-WO3 NPs) modified by aminopropyl triethoxysilane (APTES) was created and coated on the alumina ceramic support surface via interfacial polymerization, in which the material covalently cross-links on the membrane's active layer in the presence of terephthaloyl chloride (TPC) as a cross-linker and piperazine (PIP) as an external amine. Achieving a unique combination of oil and water surface wettability- superhydrophilicity (0° water-in-air contact angle) and underwater super-oleophobicity (160.25° under-water oil contact angle) was the key to creating the water-permeating NH2-WO3/PA@alumina ceramic membrane. The second advantageous feature of the membrane is its capacity for self-cleaning, which results from WO3 NP's innate photocatalytic activity that has been further enhanced by amino functionalization. A water permeate flux of up to 250 L m−2 h−1 and an oil/water separation efficiency of nearly 100 % were attained for an oil concentration of 50 ppm of crude oil-in-water emulsion when NH2-WO3/PA@alumina ceramic membrane was employed as a separation medium in a cross-flow filtration system for the separation of crude oil-in-water emulsion. Furthermore, the permeate flux decreased to ∼25 % of its initial flux after using NH2-WO3/PA@alumina ceramic for approximately 210 min. This was caused by organic pollutants in the oily water clogging the membrane pores. The permeate flux was recovered by exposing the membrane to UV light for photo-catalytic self-cleaning. Due to its water-passing nature, this membrane has high efficiency. Additionally, because the self-cleaning add-on removes the need for chemical cleaning, it is environmentally friendly.

Facile fabrication of expanded graphite/polydimethylsiloxane foams for oil–water separation

3D porous foams for oil–water separation via selective adsorption were obtained by incorporating expanded graphite (EG) granules into polydimethylsiloxane (PDMS) foams. The EG@PDMS6-t foam prepared with a PDMS:EG and NaCl:PDMS mass ratio of 6:1 and 8:1, respectively, possesses a high porosity of 80.3%, a water contact angle of 127.7°, and an oil contact angle close to 0°. The foam exhibits an impressive adsorption capacity towards light oil (hexane,6.28 g/g), heavy oil (trichloromethane, 13.33 g/g), and kitchen waste oil (4.51 g/g), being able to separate 100% of oils from an immiscible oil–water mixture and 39.0% of camellia oil and 45.3% of kitchen waste oil from oil-in-water emulsions via selective adsorption. The foams possess excellent elasticity and desirable reusability in oil–water separation and exhibit outstanding resistance to acidic and alkaline environments. EG accounts for 96.5% of the EG@PDMS6-t foam’s volume. SiO2@PDMS hydrophobic layer was constructed on the top of EG@PDMS6-t foams by a spraying technique to tailor-make 3D filters for oil–water gravity-driven separation. The P20s-S0.2-EG@PDMS6-t filter shows an excellent immiscible trichloromethane-water gravity-driven separation, with a trichloromethane permeate flux of 11,024 L/m2h, a water rejection time of 60 s, and a separation efficiency of 99.7%. The filters are highly robust to chemical corrosion and tape-peeling.

Oil/water separation copper membranes modified by laser induced ZnO nanowires growth with enhanced catalytic function

Oil/water separation is a significant area of scientific study, and also has significant practical applications in the treatment of industrial oily wastewater and oil spill pollution. In this study, the high-flux copper mesh is fabricated by laser in a Zn2+ precursor solution at room temperature. The copper mesh processed inside the solution has a higher flux than that processed in the air. The heat absorbed by the liquid promotes the growth of ZnO nanowires on the copper mesh surface. The copper mesh's underwater oil contact angle (OCA) is as high as 150°. Compared with conventional copper mesh, it has a higher stability and can maintain a contact angle of 150° in acid-base environments and high-temperature environments. It has hydrophilic and oleophobic properties and can be used for oil/water separation. After 50 oil/water separation cycles, the separation efficiency can keep higher than 97%. This new method exhibits excellent potentials for oil/water separation and oil purification attributed to its simple and ecologically friendly processing.

Controllable self-foaming preparation of durable superhydrophobic/superlipophilic polyurethane sponge for efficient oily emulsions separation

Superhydrophobic polyurethane (PU) sponges as ideal absorbent materials have attracted significant interest for oil/water separation while their durability is dramatically limited by the poor mechanochemical stability. In this work, a durable superhydrophobic sponge with special hierarchical micro/nano was fabricated by in-situ anchoring of expanded graphite (EG) and TiO2 particles under polarity-induced phase separation during facile self-foaming process. After maturation for 3 h, the prepared sponge exhibited asymmetric wettability with the water contact angle (WCA) was up to 157.9 ± 1.5° and oil contact angle (OCA) was 0°, which could selectively absorb diverse oils range from 11.48 to 41.60 times of its own weight and oily emulsion separation efficiency was up to 99.80 %. In addition, due to the enhancement of the interface bonding force between the prepared sponge skeleton and EG@TiO2 particles through the crosslinking of foaming resin during the self-foaming process, the absorption capacity of the prepared sponge decreased by only 3.74 % and the stress attenuation was only 14.10 % after 150 absorption cycles, indicating its excellent recyclability and mechanical stability. Notably, when subjected to the harsh environment including acid/alkali conditions, high temperatures, salt solutions and organic solvents, the prepared sponge could remain stable superhydrophobicity with the WCAs all over 154.4° ± 1.5°, demonstrating its excellent chemical stability. Besides, PU/EG@TiO2 sponge demonstrated prominent antifouling and self-cleaning properties. Overall, this work provided an advanced idea for the preparation of superhydrophobic sponge with outstanding mechanochemical stability, which exhibited great potential in the treat of oily emulsified wastewater.

Design and fabrication of ordered silicon micro/nano-hybrid hierarchical structures decorated by silica thin layer for superantiwetting surface

The wetting properties of micro/nano-hybrid hierarchical structures offers important applications in many fields. However, the fabrication of hierarchical micro-nanostructures still suffers the limitations of complicated fabrication process, high cost and small area. Here, we develop a novel strategy for the fabrication of uniform micro/nano-hybrid hierarchical silicon structures by combining the photolithography, thermal de-wetting and metal-assisted chemical etching (MACE). The outstanding advantage of this technique is the ability to achieve nano-patterning at the full 4″ or 6″ wafer scale in a very facile and affordable manner, regardless of the substrate surface topography. Moreover, nanostructures generated by this technique can be customized independently at a specific level with very high feature control. By oxidizing the structure and modifying it with specific functional groups or molecules, the wettability of the surface can be transformed from the underwater superoleophobic state with an oil contact angle (OCA) of ∼169° to underwater superoleophilic state (an OCA of ∼8.4°). The transition from superhydrophobic state with a water contact angle (WCA) of ∼175.5° to quasi-superhydrophilic state (a WCA of ∼10.5°) can also be achieved, which is highly desirable for optoelectronics, environment, and biomedicine fields.

Versatile Application of TiO2@PDA Modified Filter Paper for Oily Wastewater Treatment

Although membrane separation technology has been widely used in the treatment of oily wastewater, the complexity and high cost of the membrane preparation, as well as its poor stability, limit its further development. In this study, via the vacuum-assisted suction filtration method, polydopamine (PDA)-coated TiO2 nanoparticles were tightly attached and embedded on both sides of laboratory filter paper (FP). The resultant FP possessed the typical wettability of high hydrophilicity in the air with the water contact angle (WCA) of 28°, superoleophilicity with the oil contact angle (OCA) close to 0°, underwater superoleophobicity with the underwater OCA greater than 150°, and superhydrophobicity under the water with the underoil WCA over 150° for five kinds of organic solvents (carbon tetrachloride, toluene, n-hexane, n-octane, and iso-octane). The separation efficiency of immiscible oil/water, oil-in-water, and water-in-oil emulsions using the modified FP is higher than 99%. After 17 cycles of emulsion separation, a high separation efficiency of 99% was still maintained for the FP, along with good chemical and mechanical stability. In addition, successful separation and purification were also realized for the oil-in-water emulsion that contained the methylene blue (MB) dye, along with the complete degradation of MB in an aqueous solution under UV irradiation.

Preparation of carbon-based active nanofluids with temperature and salt resistance for enhanced oil recovery

The abundant hydrophilic surface groups endow carbon-based nanoparticles (CDs) with intrinsic great dispersibility, however, the strong hydrophilicity limits the oil–water interface activity, restraining the performance in enhanced oil recovery. Developing CDs with simultaneously ultra-small sizes, high temperature and salt tolerance, as well as superior interfacial activity is of great significance. In this work, CDs with the size of 3.3 nm and excellent temperature and salt resistance were prepared by hydrothermal reaction, using citric acid (CA) and ethylenediamine (EDA) as precursors. Carboxyl ether carboxylate-6Na (APEC-6Na) was selected as the compound agent to construct carbon-based active nanofluids (CANs) with excellent oil–water and oil-solid interfacial activities. CANs can reduce the oil–water interfacial tension to 8.9 × 10-4 mN m−1, withstand a temperature up to 90°C and a salinity up to 6.3 × 104 mg·L-1. Even at the highest tolerant salinity, the underwater oil contact angle of 155° can be achieved, demonstrating excellent wettability control capability, which could be attributed to the synergistic effect of the compound CANs system. The increase of the contact angle of underwater oil droplets facilitates the coalescence of oil film on the lipophilic surface to form oil droplets. The electrostatic repulsion generated by the adsorption of CDs and APEC-6Na at the oil–water interface and rock surface makes the coalesced oil droplets more easily detached from the rock surface, and the oil film reduction rate exceeds 97.7 % within 24 h. The excellent oil–water and oil-solid interface properties and the structural separation pressure endows CANs with remarkable performance in core displacement experiments. Compared with simulated formation water, CANs can improve the recovery rate by 26.3 %, exhibiting important application value for improving the recovery rate of ultra-low permeability reservoirs.

Fabrication of superhydrophobic melamine sponge composite sorbent in supercritical carbon dioxide atmosphere for selective and effective oil removal from water

In this study, both the modification of activated halloysite nanotube (HNT) with methyltriethoxysilane (METES) and the fabrication of durable, superhydrophobic (water contact angle: 153.0°) and superoleophilic (oil contact angle: 0 °) melamine sponge (MS)-HNT-METES sorbent material (MS-METES) were achieved in supercritical carbon dioxide (scCO2) atmosphere. For the coating of MS with clay mineral and METES through sol-gel reaction in scCO2, optimal process conditions were determined to be pressure difference of 60 bars at 35 °C, solvent/METES mass ratio of 7.5, METES/MS mass ratio of 10, and degas time of 400 s. Successful preparation of MS-METES was proven by XPS, FTIR, 29Si-MAS NMR, SEM, and contact angle measurements. MS-METES displayed excellent sorption capacity for various petroleum products, oils, and organic solvents (49.6–122.4 g/g), remarkable oil-water separation efficiency (99.1%, for continuous separation technique), high selectivity for oil/organic solvent in acidic, salty, and alkaline solution conditions, good reusability, chemical stability and robustness, and outstanding flexibility and mechanical stability. We believe that the innovative process used in this study will have great potential to be used by researchers in the direct fabrication of new superhydrophobic and superoleophilic sorbent materials for the selective removal of oil and organic solvent spills from water.

A facile approach for oil-water separation using superhydrophobic polystyrene-silica coated stainless steel mesh bucket

Inspired by traditional shaduf technology in the irrigation field, we fabricated a superhydrophobic stainless steel mesh bucket by layering polystyrene and SiO2 nanoparticles through a facile dip coating technique for effective oil-water separation. The superhydrophobic steel mesh bucket could effectively lift oil as well as microplastic pollutants from the water surface. The water contact angle of a two-layered polystyrene-silica coating was 158.5° ± 2°, while the oil contact angle was nearly 0°. The oil-water separation performance of superhydrophobic mesh was tested using several kinds of oil. The separation efficiency achieved for low viscous oil was 99.33 %, while 86.66 % efficiency was recorded for high viscous oil. The superhydrophobic mesh showed high durability against mechanical tests including bending, folding, twisting, adhesive tape tearing (25 cycles), and sandpaper abrasion (20 cycles). The mesh presented admirable thermal and chemical durability. The present superhydrophobic steel mesh bucket is a suitable candidate for large-scale application.

Antifouling multi-functional membrane for oil/dye wastewater treatment: Regeneration while treating mixed pollutants

Treatment of insoluble oils or soluble organic dyes in wastewater by membrane separation is considered to be one of the most effective strategies. However, simultaneously removing oils and dyes from wastewater is challenging. In this study, hydroxyl iron oxide was grown on PVDF membranes by in situ self-assembly and in situ self-growth strategies using proanthocyanidins as a bridge. The PVDF-PC-FeOOH membrane possesses excellent wettability and photo-Fenton catalytic properties (all types of underwater oil contact angles are larger than 150°, and the degradation efficiency of methylene blue within 20 min is greater than 70%). The emulsion separation flux and efficiency can reach 976.1 L·m-2h−1 and 99.7%, respectively. In addition, the photo-Fenton catalytic degradation process was discussed. The regeneration rate of the membrane is over 90%. The flux can be stabilized over a period of time in a continuous filtration process of 60 min (flux over 158.7 L·m-2h−1). Simultaneous removal of mixed pollutants and regeneration of the membrane is achieved in a single step. In multi-component oily wastewater, the membrane has selective adsorption capacity for cationic dyes, and the removal rate can achieve 98.6%. The strategy provided in the present study enhances the value of membranes for practical applications in the field concerning the filtration of oily wastewater and selective separation of dyes in the dyeing and printing industry.

Tribological behavior of squamous textured SiC sliding against graphite under mixed lubrication

Texturing of sealing faces is an effective approach to reduce wear failure and improve the working efficiency and service life of mechanical seal, particularly under insufficient lubrication. Herein, a silicon carbide surface with a novel squamous texture is fabricated using laser. A reciprocating pin-on-disk wear test is conducted on silicon carbide and graphite surfaces to investigate the tribological properties of squamous texture arrangements and parameters under mixed lubrication. Results demonstrate that the symmetrical and evenly distributed texture arrangement displays remarkable load-carrying capacity. Appropriate adjustment of texture parameters can achieve a considerably low oil contact angle. The squamous texture with a major to minor axis ratio of 1.5 has the excellent tribological properties, reducing the average coefficient of friction by 26.7 %. Moreover, the squamous texture facilitates the formation of a graphite transfer film and traps debris, which helps avoid particle and adhesive wear, resulting in a low wear rate. However, high pressure nullifies the hydrodynamic effect and accelerates the shearing of graphite asperities, thereby increasing friction and wear. This study provides a novel strategy for enhancing the tribological behavior of sealing surfaces.

Superhydrophobic PODS-modified nickel foam with reversible wettability for oil-water separation

In this work, superhydrophobic and superoleophilic nickel foam was fabricated to effectively purify oil-water mixtures. Octadecyltrichlorosilane (OTS) was utilized to form polymerized octadecylsiloxane (PODS) coatings on the nickel foam through hydrolysis and subsequent polycondensation reactions. The surface composition and morphology of the nickel foam were characterized using Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The initially smooth surface of the nickel foam became rough upon being coated with the PODS. The incorporation of long alkyl chains from the PODS coating, along with the introduced roughness, synergistically provided the nickel foam with superhydrophobic and superoleophilic properties. The PODS-modified nickel foam demonstrated a water contact angle (WCA) of 151.3° and oil contact angle (OCA) of 0°, exhibiting excellent wettability selectivity towards water and oil. Additionally, it showcased a remarkable permeation flux of 7468.4 ± 236.3 L·m−2·h−1 when tested with a water-n-hexane emulsion. This superior performance enabled efficient separation of oil and water. Notably, even after 20 cycles, the PODS-modified nickel foam maintained a separation efficiency of over 98.4 %. Furthermore, the wettability of the PODS-modified nickel foam could be easily switched from superhydrophobicity to superhydrophilicity through a straightforward prewetting treatment using ethanol. In this process, ethanol served as a mediator between the hydrophobic surface and water. Once the prewetted foam was thoroughly dried, the hydrophilic channels were eliminated, thus restoring the superhydrophobicity of the nickel foam. This reversible transition of wettability holds great potential for the development of smart filters capable of effectively addressing diverse challenges in oily wastewater treatment.

Fabrication of a superhydrophobic-superoleophilic particle material for oil-water separation and oil extraction

Oil-water separation has become a serious issue due to the increasing oily wastewater discharged in the environment and oil spills from time to time. Superhydrophobic and superoleophilic materials are a promising approach in oil-water separation. However, the preparation procedures for these materials are often complex and expensive, and their stability is not robust enough. In this study, superhydrophobic and superoleophilic particles are successfully prepared via a facile and green mixing method. Fluorocarbon resin, CaCO3 and SiO2 are coated on fly-ash cenospheres to form a stable superhydrophobic-superoleophilic surface, which exhibits a water and oil contact angle of 153.3° and 0°, respectively. To our knowledge, we’re unaware of any previous study reporting a superhydrophobic-superoleophilic material prepared in such a convenient way. The as-prepared superhydrophobic material can serve as high-performance filters for separating various oil-water mixtures, with a separation efficiency up to 99.2%. And it can be applied in water-in-oil emulsion separation. Meanwhile, the as-prepared particles are able to extract oils from oil-water mixtures and the oil-extraction capacity is up to 0.56 g/g. Furthermore, the obtained material has a robust stability against various hash conditions and a good recyclability. The simply-prepared superhydrophobic cenospheres are expected to be a promising candidate for application in diverse oil-water separation situations.